High-resolution tiles
Raster tiles
High-resolution tiles (often also called "retina" tiles) are raster tiles with a higher resolution than usual. This is a configuration feature of the tile server software.
Devices with a high-resolution display (more than 100 dpi) benefit from retina tiles because the map looks nearly as sharp as the rendered user interface around it. On screens high-resolution tiles have the effect of making everything in the image look exactly the same but bigger (it might feel like you're seeing less detail). When printing, this means you get more dots per inch, sharper print quality, but without scaling down things like text labels to become too small.
The scaled-up features of high-resolution tiles (text in bigger fonts, larger icons) will help with visual impairment.
The same coverage area with the same number of pixels, but on the right we see a standard zoom level 16 rendering, on the left we use these pixels to display fewer features, equivalent to what would normally be rendered smaller at zoom level 15. With more pixels these features appear sharper, more defined, and bigger
Larger animated comparison
Slippy maps may be configured to show such tiles in a scaled down size by default and the user's browser can enlarge them again if it is set to enlarged web pages (including images). Or maybe the slippy map software could read the user's dpi setting and scale accordingly (just an idea …). This may be useful on high-resolution displays to achieve resolution independence for slippy maps.
Examples
- side-by-side comparison of standard and retina tiles
- retina tiles by lyrk
- RRZE test service presenting double resolution maps (but scaled to normal size in this view. This is a "retina" presentation which will look good on a mobile).
- The idea is also illustrated nicely here in relation to the geofrabrik WMS service (paid for).
- BBBike map compare with retina maps
- a highres tile map by OsmAnd
- Mapbox APIs for map tiles and static map images have an option to return Retina (2×) images.
- Thunderforest has a collection of different map types with retina support. Free for the first 150,000 tile requests per month
Vector tiles
Vector tiles are shipped as vector data to the client and therefore are not directly bound to a defined resolution. They are an alternative for simple maps and mobile devices because the rastering usually happens on client side.